GENEVA - A new coronavirus has now claimed 22 lives worldwide out of 44 lab-confirmed cases, mostly in Saudi Arabia, World Health Organization officials said Thursday.

The latest fatal case of the Middle East respiratory syndrome coronavirus, or MERS, involves a 63-year-old man with an underlying medical condition who died Monday, five days after being hospitalized with acute breathing problems, WHO officials told the annual World Health Assembly in Geneva.

"There is a huge amount that we do not understand about this virus or this situation," Dr. Keiji Fukuda, WHO's assistant director-general for health security, told hundreds of health officials.

He said the newest fatality occurred in central Saudi Arabia, and is not related to the cluster of cases reported from the country's east.

Four of every five of the 44 confirmed cases affects a man and the patients' average age is 56, said WHO officials, citing information that comes in part from Saudi health authorities. Patients have been between the ages of 24 and 94.

Saudi authorities have reported 10 deaths from 22 cases since an outbreak began at a health care facility in April in the country's east, WHO officials said.

Tunisia authorities have reported two confirmed cases, involving a brother and sister, and one probable case involving their 66-year-old father, who died in Tunisia on May 10, a week after returning from Saudi Arabia and Qatar, the officials said.

"We do not know the full geographic spread of this virus," said Fukuda, who told the assembly that the incubation period seems to be anywhere from 2 1/2 days to 14 days.

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